Storage tank shutoff valve

ABSTRACT

A valve assembly for automatically shutting off the flow of a pressurized liquid to a storage tank includes a cam that is rotated in response to the level of a liquid in the storage tank. A follower moves a poppet valve axially with a housing as a nonlinear function of rate of cam rotation. The poppet valve is moved to a closed position to terminate flow of a liquid to the storage tank whenever the liquid level within the storage tank reaches a predetermined level.

TECHNICAL FIELD

The present invention relates generally to valves and more particularlyto a shutoff valve assembly for automatically cutting off flow of aliquid to a storage tank in response to a predetermined fluid level inthe storage tank. The invention will be specifically disclosed inconnection with a valve assembly that is especially adapted for use witha pressurized supply line and that minimizes line shock in the fluidsupply line during valve closing.

BACKGROUND OF THE INVENTION

It is very common practice to use liquid storage tanks for such fluidsas gasoline, diesel fuel, and oil. These storage tanks are usuallyfilled through openings that extend upwardly from the top of the tanks.Such openings usually have relatively small diameters that are sized toreceive a dispensing tube, which dispensing tube is connected to a tanktruck or other supply source. In most cases, these storage tanks do nothave gauges and the operator filling the storage tank has no visualaccess to the internal space of the storage tank, or any other reliableway of determining when the storage tank is approaching a full level. Asa consequent of these factors, overfilling of the storage tanks is acommon occurrence. Such overfilling of a storage tank may result inspillage of the tank contents, damage to the tank or filling equipment,or injury to persons. Concerns over spillage of the tank contents isparticularly acute when the contents are flammable, toxic, or otherwisepotentially dangerous or environmentally hazardous. The problemsassociated with overflow spillage have become so widespread that manylocal governments now require some liquid storage tanks to be filledonly with equipment that automatically shuts off the flow of the flow ofliquid to the storage tank when the tank is full.

One way to automatically shutoff the flow of liquid to a full storagetank that has been employed in the prior art is to place a shutoff valvein the dispensing line used for supplying liquid to the storage tank.These types of shutoff valves usually employ floats that are moved by arising liquid level in the tanks. The movement of the floats is, inturn, used to move a closure element in the shutoff valve from an openposition to a closed position that stops or significantly reduces theflow of fluid through the drop tube. Examples of such shutoff valves indrop tubes are illustrated in U.S. Pat. No. 4,986,320 to Kesterman et.al. and U.S. Pat. No. 4,667,71 to Draft.

The shutoff valves described above perform very satisfactorily forunderground storage tanks where the tanks are filled only under gravitypressure, which pressure is typically in the range of 4 to 5 psi.However, such shutoff valves are unsuitable when above ground storagetanks are used, or when, for any other reason, pumping pressure (notmerely gravity pressure) is used to drive the fluid being introducedinto the storage tanks. A typical pump used for driving liquid to anabove ground storage tank delivers liquid at a pressure of approximately50-60 psi, more than ten times the pressure encountered in gravity feedsystems. Among other difficulties involved when such pumping pressureare used is the increased potential for line shock in the supply hoseand related components. When a valve is closed rapidly, the flow throughthe valve is reduced sharply, and the pressure on the upstream side ofthe valve increased correspondingly. This action results in a shock waveof high pressure that is propagated upstream, applying high pressurepulses to the supply line and all of its related components. If thevalve is closed sufficiently rapidly, the shock wave resulting from thatclosure may damage, or even rupture, the supply line and result inleakage. Because of the increased pressure conditions associated withthe filling of above ground storage tanks, both from operating the valvecomponents under the increased dynamic pressures of the fluid during thefilling process and the increased line shock resulting from valveclosure, shutoff valves used for underground storage tanks havegenerally proved to be unsuitable for use in above-ground tanks.

There have been at least two commercialized attempts in the prior art tosolve the problems associated with shutoff valves for above groundstorage tanks and the increased pressures involved therewith. In one ofthese attempts, a drop tube is provided with a shutoff valve located atits lower terminus. The valve includes circumferential outlet ports. Afloat is slidably fitted on the outside surface of the drop tube, andthe float is interconnected to a restrictor sleeve for common movementtherewith on the drop tube. As increased fluid levels occur in thestorage tank, the float, and thus the restrictor sleeve, is urgedupwardly. This upward movement of the restrictor sleeve positions itover the circumferential outlet ports of valve, restricting furtherfilling of the storage tank. Among other deficiencies, this type ofshutoff valve relies solely on gravity for returning the float to anopen position once liquid in the storage tank is depleted. Thus, it isproned to reset failure. Moreover, this method of shutting off fluidflow inherently requires the shutoff valve to be near the bottom of thedrop tube, making it prone to clog-up from solid matter that typicallysettles in the bottom of storage tanks. Still further, such valves donot completely shut off the flow of liquid into the storage tank.

In another less than fully successful prior art attempt to solve theabove described problems, a plug valve is disposed in a drop tube. Theplug valve includes a rotatable plug member that is connected by rods toa float. As the fluid level in the storage tank is increased, the floatcauses the connecting rods, and thus the rotatable plug, to rotate. Thistype of shutoff valve arrangement has the disadvantage of significantlyreducing fluid flow when partially closed, and thus significantlyslowing down the filling last portion of the filling process.Furthermore, this valve relies only on the weight of the float to returnthe valve to an open position once fluid in the storage tank is removed.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the invention to provide a valveassembly suitable for shutting off the flow of a high pressure liquidthat is being pumped into a storage tank in response to a predeterminedliquid level in the storage tank.

It is another object of the invention to provide a valve assembly thatcontrols the movement of a shutoff valve in a supply line furnishingliquid to a storage tank as a predetermined nonlinear function of thelevel of fluid in the storage tank.

Another object of the invention is to provide a valve assembly forsimultaneously maximizing the flow of liquid into a storage tank andminimizing the line shock resulting from rapidly shutting off the liquidflow into the storage tank.

A still further object of the invention is to provide a valve assemblythat protects a shutoff valve in a supply line to a storage tank fromthe dynamic forces of supply line flow.

Another object of the invention is to minimize the friction associatedwith the movement of a shutoff valve that is moved in response to aliquid level in a storage tank.

Additional objects, advantages, and other novel features of theinvention will be set forth in part in the description that follows andin part will become apparent to those skilled in the art uponexamination of the following or may be learned with practice of theinvention. The objects and advantages of the invention may be realizedand attained by means of the instrumentalities and combinationsparticularly pointed out in the appended claims.

To achieve the foregoing and other objects, and in accordance with thepurposes herein, an improved high pressure shutoff valve for a storagetank is provided for cutting off the flow of a fluid into a storage tankor the like in response to a predetermined fluid level in the tank. Theassembly includes a housing adapted for placement in a storage tank. Thehousing has an inlet and an outlet and an internal axial flow passagetherebetween. A valve assembly is disposed in the housing. The valveassembly includes a shutoff valve movable within the housing in an axialdirection between a first open position permitting the flow of fluidthrough said internal flow passage and a second closed positionsubstantially blocking fluid flow through said internal passage. A guideassociated with the housing is provided for guiding movement of theshutoff valve in the axial direction. An actuating assembly isinterconnected to the valve assembly for moving the shutoff valvebetween its open and closed positions as a nonlinear function of a fluidlevel in a storage tank.

The assembly includes a shield disposed within the housing's internalflow passage between the inlet and the shutoff valve. This shieldprotects the shutoff valve from direct fluid impingement from fluidentering the internal flow passage through the housing inlet. The shieldis concentrically disposed about the shutoff valve.

According to one aspect of the invention, the actuating assemblyincludes a float for sensing the level of a fluid in storage tank, a camrotatable as a function of the position of the float, and a cam followerthat is axially movable as a nonlinear function of the rotatableposition of the cam.

In the preferred form of the invention, the shutoff valve is a poppetvalve with a generally cylindrical outer sidewall, and the shield has aninternal sidewall in spaced, generally parallel relationship to theouter sidewall of the shutoff valve. The space between the outer wall ofthe shutoff valve and the internal sidewall of the shield forms acontrolled leak path from the internal axial flow passage to the reliefvalve.

In another aspect of the invention, a relief valve also is provided. Therelief valve is resiliently biased to an open position, and is urged toa closed position in response to pressure of fluid that has passedthrough the controlled leak path.

According to yet another aspect of the invention, the valve stemincludes an internal flow path for providing selective fluidcommunication between the controlled leak path and the interior of thestorage tank. The relief valve is operative to selectively block fluidcommunication between the controlled leak path and the internal flowpassage of the valve stem.

According to still another aspect of the invention, the volumetric flowcapacity of the internal flow path of the valve stem is greater than thevolumetric flow capacity of the controlled leak path.

The shutoff valve preferably is resiliently biased to a closed positionand arranged so that downward movement of the float overcomes theshutoff valve bias and forces the shutoff valve to an open position.

In still another aspect of the invention, the housing is interposedbetween first and second dispensing line segments with the housing inletbeing in fluid communication with the first dispensing line segment andthe housing outlet being in fluid communication with the seconddispensing line segment. The float is concentrically disposed about thesecond dispensing line segment.

In accordance with another aspect of the invention, the internal flowpath of the valve stem has an inlet at the upper axial end of the valvestem and a radially extending outlet intermediate its axial ends. Theguide includes a circumferential groove for receiving fluid from theinternal flow path of the valve stem. The circumferential groovecommunicates with the interior of the storage tank at a level above theliquid level in the storage tank required to move the shutoff valve to aclosed position.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, incorporated in and forming a part of thespecification, illustrate several aspects of the present invention, andtogether with the description, serve to explain the principles of theinvention. In the drawings:

FIG. 1 is an environmental view showing an automatic shutoff valveconstructed in accordance with the principles of the present inventionas it is used to fill an above-ground storage tank from a tank truck;

FIG. 2 is a enlarged perspective view, partially in section, depictingthe automatic shutoff valve shown of FIG. 1 in a fully open position;and

FIG. 3 is enlarged perspective view of the shutoff valve of FIG. 1,similar to the illustration of FIG. 2, but showing the shutoff valve ina closed position.

Reference will now be made in detail to the present preferred embodimentof the invention, an example of which is illustrated in the accompanyingdrawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings, FIG. 1 shows a tank truck, generallydesignated by the numeral 10, for transporting a flammable liquid, suchas gasoline or oil, as it is parked next to an above-ground storage tank12. The illustrated tank truck has a liquid pump 14 on its underside forpumping the tank truck's liquid contents from a first positioncorresponding to the height of the tank truck discharge, which istypically 18 inches to two feet off the ground, to second elevatedposition above the height of the storage tank 12. Depending on the typeof storage tank involved, this second elevated position tank may be, ina typical situation, at a height of six feet or more above ground level.

The liquid from the tank truck 10 is pumped to the second elevatedposition above the storage tank 12 through a dispensing line 16. Thisdispensing line is connected to the pump 14 through the agency of aninternally threaded coupling 18 on the end of the dispensing line, whichcoupling is threadably received by an externally threaded outlet nippleof the pump 14. As shown, the dispensing line 16 has a first horizontalsection 16a for transporting the tank truck contents to a locationadjacent to the side of the storage tank 12, a first vertical section16b for transporting the liquid to a height above the storage tank, asecond horizontal section 16c for transporting the liquid over thestorage tank 12, and a second vertical section 16d for directing theliquid downwardly into the storage tank's interior.

The storage tank 12 has a first riser 20 formed by an upstanding bossthat circumscribes a closable fill opening on its top side. This firstriser 20 defines a fill aperture 22 adapted to receive the secondvertical section 16d of the dispensing line 16. In the illustratedembodiment, the aperture 22 has a diameter of approximately 6 inches. Asis well known in the art, the illustrated storage tank 12 also has asecond riser 24 circumscribing a second closable opening foraccommodating the entry of a vapor recovery line 26 for returning to thetank truck vapors displaced by the introduction of liquid into thestorage tank 12, and a vent 28 for exhausting excess pressure from thestorage tank 12.

In accordance with the principles of the present invention, the secondvertical section 16d of the dispensing line 16 includes an automaticshutoff valve assembly 30 for shutting off the pressurized flow of theliquid from the tank truck 10 whenever the level of liquid in thestorage tank 12 reaches a predetermined level. This automatic shutoffvalve assembly 30 is shown in substantially greater detail in FIGS. 2and 3, from which it can be seen that the shutoff valve assembly 30 ofthe preferred embodiment includes a housing 31 having a central section32 with a generally cylindrical configuration. The upper portion of thiscentral section 32 is disposed within a collar 34 that fits within thefill aperture 22 and seals the aperture against leakage of vapors. Thecentral section of the particular valve assembly housing 31 illustratedhas a diameter of approximately four inches and includes connector necks36 and 38 of reduced diameter on its upper and lower axial ends. Each ofthese connector necks 36, 38 provides an axial opening to or from theinternal space of the housing 31 and is internally threaded tothreadably receive and interconnect with segments 16e and 16f of thesecond vertical dispensing line. In the specific size of valve assembly30 illustrated in the drawings, the central portion of the housing 31has a diameter of approximately 4 inches, with each of the illustrateddispensing line segments 16a16f having a diameter of approximately twoinches. When connected to the dispensing line segments, these connectornecks 36 and 38 respectively define an inlet 40 and an outlet 42 for thehousing.

The housing 31 has an internal flow passage 44 that extends between theinlet and outlet. Fluid flow through this internal flow passage iscontrolled by a valving assembly, generally designated by the numeral48. The valving assembly 48 includes a shutoff valve 50 that, as will beexplained in greater detail later, is used to terminate flow through theinternal flow passage 44 of the housing 31 when the fluid level in thestorage tank 12 reaches a predetermined level. In the preferred form ofthe invention illustrated in FIGS. 1-3, the shutoff valve 50 takes theform of a poppet valve that moves axially within the housing 31. Thispoppet valve 50 has a horizontal section 50a that extends radiallyoutwardly from a centrally disposed threaded opening 52 to an upwardlyextending sidewall section of cylindrical configuration 50b. Theupwardly extending sidewall section 50b of the shutoff valve 50 isconcentrically positioned with respect to the generally cylindricalhousing (12) sidewalls.

The illustrated shutoff valve 50 is rigidly connected at its centrallydisposed opening 52 to, and moved by, a valve stem 54. The connectionbetween the shutoff valve 50 and the valve stem 54 is achieved byproviding threads on the upper axial end of the valve stem 54, andthreadably interconnecting that upper axial end to the centrallydisposed opening 52 of the shutoff valve 50. A stem guide 56 controlsmovement of the valve stem 54, and thus insures that the poppet valve 50moves in the direction of the axis of the housing 31. The stem guide 56is centrally supported within the internal flow passage 44 by stem guidesupports 58, which stem guide supports 58 are rigidly attached to andextend radially inwardly into the center of the internal flow passage 44from the internal sidewall of the housing 31.

As is visually apparent from jointly viewing the illustrations of FIGS.2 and 3, the shutoff valve 50 is movable from a first open or unseatedposition (illustrated in FIG. 2) in which the shutoff valve 50 permitsfluid flow through the internal flow passage 44 of the housing 31 to asecond closed or seated position (illustrated in FIG. 3.) in which fluidflow through the passage 44 is substantially blocked. In the second orclosed position of FIG. 3, the outer periphery of the lower surface ofthe horizontal section 50a of the shutoff valve 50 engages and seatsagainst a valve seat 60. As illustrated, the valve seat 60 includes acircumferential support 60a that extends radially inwardly from theinternal surface of the housing 31 to define a circular aperture 62within the housing's internal flow passage 44. A raised bead 60a extendsaxially upwardly from the circumferential support about the aperture 62to form a contact surface against which the lower surface of the shutoffvalve 50 seats.

According to another aspect of the invention, the shutoff valve 50 isprotected from the dynamic forces of pressurized flow impingementthrough the housing by a cup-shaped bonnets or shield 66. This bonnet 66has a first generally horizontal section 66a that extends radiallyinwardly in a plane located proximal to the housing inlet 40. Thehorizontal section 66a of the bonnet is joined about its entire outerperiphery by an axially downwardly extending sidewall section 66b. Forreasons that will be explained in greater detail below, the bonnet 66 isconcentrically disposed with respect to the shutoff valve 50 to form acontrolled leak path between the shutoff valve 50 and the bonnet 66.This controlled leak path is accomplished in the illustrated embodimentby positioning the downwardly extending sidewall section 66b of thebonnet in closely spaced, parallel relationship to the upwardlyextending sidewall section 50b of the shutoff valve. The bonnet 66 issupported by a bridge structure 68 consisting of two supports thatextend between the internal sidewall of the housing 31 and thedownwardly extending sidewall 66b of the bonnet.

The valve stem 54 has an internal flow passage that extends between aninlet 70 in its upper axial end and a radially extending outlet 72intermediate its ends. The radially extending outlet is disposed withina circumferential groove 74 in the valve stem guide 56. Thecircumferential groove 74 empties into a radial passageway 76 that flowsoutwardly through the housing 31 to the interior of the storage tank 12.

The threaded upper axial end of the valve stem 54 also is threadablyconnected to a check ball retainer sleeve 78, which check ball retainersleeve 78 has a tubular configuration with an internally threaded lowerportion. This lower portion of the check ball retainer sleeve 78 isscrewed onto the upper axial of the valve stem 54 on top of the poppetvalve 50. A check ball 80 is retained in the check ball retainer forselectively seating against the axial upper end of the valve stem 54 andblocking liquid flow into the valve stem's internal passageway. Thecheck ball 80 is movable between a first open position, depicted in FIG.2, in which liquid flow into the axial end of the valve stem 54 ispermitted, to a second closed position, depicted in FIG. 3, in which thecheck ball 80 blocks liquid flow into the passageway. A firstcompression spring 82 extending between the lower planar surface of thebonnet 60 and the upper planar surface of the poppet valve 50 isconcentrically disposed about the check ball retainer sleeve 78 to urgethe check ball 80 to the first or open position. A second compressionspring 84 is disposed within the check ball retaining sleeve 78 to urgethe check ball 80 to its first or open position. A retaining pin 6extends across the upper opening of the check ball retaining sleeve 78to maintain the check ball 80 within the retaining sleeve 78.

The lower axial end of the valve stem 54 is attached to a yoke 88. Asdepicted in the drawings of FIGS. 2 and 3, the yoke 88 includes a pairof downwardly depending arms 88a that are joined at their upper axialends by a cross piece 88b. The arms support 88a a roller or cam follower90 that is positioned between, and rotatably connected to, each of thetwo arms 88a by a shaft 92. The roller 90 rides upon and follows theprofile of a cam 94 which is rigidly attached to a rotatable shaft 96.The lower ends of each of the yoke arms 88a have an open-ended elongated"U-shaped" groove 88c that is fitted about the rotatable shaft 96. Aswill be apparent to those skilled in the art from comparing theillustrations of FIGS. 2 and 3, these openended "U-shaped" grooves 88aallow the yoke 88 to be freely movable with respect to the rotatableshaft 96 in the vertical direction, while restricting relative movementbetween these two components 88 and 96 in all other directions.

The shaft 96 of the cam 94 extends through opposite sides of the5housing 31 sidewall and is rotatably supported by the housing 31.Crankshafts 98 (only one of which is shown) are connected to the shaft96 outside of the housing 31. These crankshafts 98 are pivotally joinedto a tubular shaped float 100 by connecting links 102 (again, only oneof which is illustrated). The float 100 is in concentrically disposedspaced relationship to, and slidably movable on, the lower segment 164of the dispensing line. By virtue of these interconnections between thefloat 100 and the crankshafts 98, vertical movement of the float, whichis effectuated by changes in the liquid level in the storage tank 12, istranslated into rotational movement of the shaft 96.

In operation, when filling a storage tank 12, the shutoff valve 50assembly is normally in the open position depicted in FIG. 2 during theinitial of a filling operation, with liquid level in the tank beingbelow the float 100. In this position of the shutoff valve 50,pressurized liquid flow exits the dispensing line segment 16e and isintroduced into the inlet 40 of the valve assembly housing 31. Afterimpinging the bonnet 66, the liquid is deflected radially outwardlyabout the downwardly depending sidewall section 66b of the bonnet andmost of the liquid passes into the opening between the shutoff valve 35and the seat 60. The liquid passing through this opening then flowsthrough the internal flow passage 44 of the housing 31, through theoutlet 42, and into the dispensing line segment 16f. In addition to theflow passing through the opening between the shutoff valve 35 and theseat 60, a small amount of flow passes in the space betweenthe..respective axial sidewall sections 50b, 66b of the shutoff valve 50and the bonnet 66, over the top of the check ball retaining sleeve 78,and into the internal flow passage of the valve stem 54. In order toinsure that flow through the valve stem's internal passage does notcreate a back pressure in the area above the shutoff valve 50, thevolumetric flow capacity valve stem passage is greater than volumetriccapacity of the controlled leakage space between the respective sidewallsections 50b, 66b of the shutoff valve and the bonnet.

As the liquid level within the storage tank 12 increases, it eventuallyreaches the level of the float 100. When the liquid level increasesfurther, the resulting buoyant force applied against the float 100 urgesthe float upwardly. This upward movement of the float 100, by virtue ofthe interconnections between the float, connecting link and crankshaftdescribed above, causes counter-rotation (as viewed from FIGS. 2 and 3)of the cam 94. In the preferred embodiment, the first sector of the camprofile forms an arc with the axis of the shaft 96 as the center point.Consequently, the initial rotation of the cam 94 does not effectuatemovement of the yoke 88, or of the shutoff valve 50. This non-movementof the shutoff valve 50 achieves several objectives. First, it initiallymaintains the shutoff valve 50 in a fully open position to maximizeliquid flow through the valve assembly. Secondly, and perhaps even moreimportantly, it insures that the initial line of force between the cam94 and the roller 90 passes through the axis of the crank 98. Thisavoids the possibility that lateral forces will be initially be appliedagainst the roller 90 and cause it to override the cam 94.

As the cam 94 is rotated further, the following sectors of the camprofile are nonarcuate and of decreasing distance from the axis of theshaft 96. As suggested from the depiction of FIG. 3, this further camrotation allows the roller 90, and thus the yoke 88, valve stem 54 andshutoff valve 50, to move axially downwardly. Such downward movementresults from downward forces applied against the shutoff valve 50 fromboth the compression spring 52 and the pressure of the liquid above theshutoff valve 50.

As downward movement of the shut off valve 50 continues with continuedupward movement of the float 100, the shutoff valve 50 advances towardthe seated position depicted in FIG. 3. When the shutoff valve 50approaches the seated position of FIG. 3, and the restriction betweenthe shutoff valve 50 and the seat 66 becomes more severe, the resultingback pressure causes increased flow into the controlled leak pathbetween the axially extending sidewalls 66b, 50b of the bonnet andshutoff valve. This increased flow exerts a corresponding increasingforce against the check ball 80. Eventually this force increases to thelevel that it forces downward movement of the check ball 80 against theresilient force of the compression spring 84. Preferably, thecompression spring 84 is match to the sizes of the valve assemblycomponents and flow rates to effectuate closure of the check ball 80immediately after the closure of the shutoff valve 50. Timing of theshutoff valve 50 and check ball 80 in this manner further facilitatesthe minimization of line shock from shutting off the flow of liquid inthe dispensing line.

In summary, numerous benefits have described which results fromemploying the concepts of the invention. The disclosed shutoff valveassembly protects the shutoff valve from dynamic flow pressure, operateseffectively under conditions of pressurized dispensing line flow, and ishighly effective in minimizing line shock that typically results fromshutting off the flow of a pressured flow of liquid into a storage tank.The disclosed shutoff valve assembly advantageously controls themovement of the shutoff valve as a nonlinear function of the liquidlevel in the storage tank and provides a pressure assisted closure ofthe shutoff valve. It also minimizes the friction required to move theshutoff valve between open and closed positions and provides a valveassembly that resets to an open position when the liquid level in thestorage tank falls below a predetermined level. The disclosed shutoffvalve assembly also advantageously bleeds off any leakage at shutoff inthe ullage above the liquid level in the storage tank, thus eliminatingthe possibility of siphoning of the liquid out of the tank.

The foregoing description of a preferred embodiment of the invention hasbeen presented for purposes of illustration and description. It has notintended to be exhaustive or to limit the invention to the precise formdisclosed. Obvious modifications or variations are possible in light ofthe above teachings. The embodiment was chosen and described in order tobest illustrate the principles of the invention and its practicalapplication to thereby enable one of ordinary skill to best utilize theinvention in various embodiments and with various modifications as aresuited to the particular use contemplated. It is intended that the scopeof the invention be defined by the claims appended hereto.

We claim:
 1. An assembly adapted for cutting off the flow of a fluidinto a storage tank or the like in response to a predetermined fluidlevel in the tank, comprising:a) a housing, said housing having an inletand an outlet and an internal axial flow passage-therebetween, saidhousing being adapted for placement in a storage tank; b) a valveassembly disposed in said housing, said valve assembly including ashutoff valve movable within said housing in an axial direction betweena first open position permitting the flow of fluid through said internalflow passage and a second closed position substantially blocking fluidflow through said internal passage; c) a guide associated with saidhousing for guiding movement of the shutoff valve in axial direction insaid housing; d) an actuating assembly, said actuating assembly beinginterconnected to said valve assembly for moving said shutoff valvebetween said open and closed positions as a function of a fluid level ina storage tank; and e) a shield stationarily secured in the internalflow passage between the inlet and the shutoff valve, the shieldincluding a radially extending portion for shielding the shutoff valvefrom direct fluid impingement from fluid entering the internal flowpassage through the housing inlet and an axially extending portion, theaxially extending portion defining a space and the shutoff valve beingmovable into the space defined by the axially extending portion of theshield.
 2. An assembly as recited in claim 1 further including a shielddisposed within said housing in the internal flow passage between theinlet and the shutoff valve for shielding the shutoff valve from dire&fluid impingement from fluid entering the internal flow passage throughthe housing inlet.
 3. An assembly as recited in claim 2 wherein theshield is concentrically disposed about the shutoff valve.
 4. Anassembly as recited in claim 3 wherein the shutoff valve is a poppetvalve with a generally cylindrical outer sidewall, and the shield has aninternal sidewall in spaced, generally parallel relationship to theouter sidewall of the shutoff valve.
 5. An assembly as recited in claim4 wherein poppet valve is axially movable within the shield.
 6. Anassembly as recited in claim 5 wherein the valve assembly furtherincludes a relief valve.
 7. An assembly as recited in claim 5 whereinthe space between the outer wall of the shutoff valve and the internalsidewall of the shield forms a controlled leak path from the internalaxial flow passage to the relief valve.
 8. An assembly as recited inclaim 7 wherein the relief valve is resiliently biased to an openposition, and is urged to a closed position in response to pressure offluid that has passed through the controlled leak path.
 9. An assemblyas recited in claim 8 further including a valve stem, the valve stembeing slidably disposed within the guide and being rigidly connected tothe poppet valve for common movement therewith.
 10. An assembly asrecited in claim 9 further including a yoke rigidly connected to thevalve stem, the cam follower being rotatably supported in the yoke. 11.An assembly as recited in claim 10 wherein the valve stem includes aninternal flow path for providing selective fluid communication betweenthe controlled leak path and the interior of the storage tank, andwherein the relief valve is operative to selectively block fluidcommunication between the controlled leak path and the internal flowpassage of the valve stem.
 12. An assembly as recited in claim 11wherein the volumetric flow capacity of the internal flow path of thevalve stem is greater than the volumetric flow capacity of thecontrolled leak path.
 13. An assembly as recited in claim 9 wherein theinternal flow path of the valve stem has an inlet at the upper axial endof the valve stem and a radially extending outlet intermediate its axialends, and wherein the guide includes a circumferential groove forreceiving fluid from the internal flow path of the valve stem.
 14. Anassembly as recited in claim 13 wherein the circumferential groovecommunicates with the interior of the storage tank at a level above theliquid level in the storage tank required to move the shutoff valve to aclosed position.
 15. An assembly as recited in claim 1 wherein theactuating assembly further includes a float for sensing the level of afluid in storage tank, a cam rotatable as a function of the position ofthe float, and a cam follower movable as a nonlinear function of theposition of the float.
 16. An assembly as recited in claim 15 whereinthe shutoff valve is resiliently biased to a closed position and whereindownward movement of the float overcomes the shutoff valve bias andforces the shutoff valve to an open position.
 17. An assembly as recitedin claim 15 wherein the housing is interposed between first and seconddispensing line segments with the housing inlet being in fluidcommunication with the first dispensing line segment and the housingoutlet being in fluid communication with the second dispensing linesegment, and wherein the float is concentrically disposed about thesecond dispensing line segment.
 18. In combination with an above groundstorage tank, an assembly for substantially terminating flow of a fluidto the storage tank in response to a predetermined fluid level in thetank, the assembly comprising:a) a housing disposed in said fluid tank,said housing having an inlet and an outlet and an internal axial flowpassage therebetween; b) a valve assembly disposed in said housing, saidvalve assembly including a shutoff valve moveable within said housing inan axial direction between a first open position permitting the flow offluid through said internal flow passage and a second closed positionsubstantially blocking fluid flow through said internal passage; c) aguide associated with said housing for guiding movement of the shutoffvalve in an axial direction and said housing; d) an actuating assembly,said actuating assembly being interconnected to said valve assembly frommoving said shutoff valve between said open and closed positions as afunction of a fluid level in the storage tank; and e) a shieldstationarily secured in the internal flow passage between the inlet andthe shutoff valve, the shield including a radially extending portion forshielding the shutoff valve from direct fluid impingement from fluidentering the internal flow passage through the housing inlet and anaxially extending portion, the axially extending portion defining aspace and the shutoff valve being movable into the space defined by theaxially extending portion of the shield.